The
PermianPermian is a geologic period and system which spans 46.7 million
years from the end of the
CarboniferousCarboniferous Period 298.9 million years ago
(Mya), to the beginning of the
TriassicTriassic period 251.902 Mya. It is the
last period of the
PaleozoicPaleozoic era; the following
TriassicTriassic period
belongs to the
MesozoicMesozoic era. The concept of the
PermianPermian was introduced
in 1841 by geologist Sir Roderick Murchison, who named it after the
city of Perm.
The
PermianPermian witnessed the diversification of the early amniotes into
the ancestral groups of the mammals, turtles, lepidosaurs, and
archosaurs. The world at the time was dominated by two continents
known as
PangaeaPangaea and Siberia, surrounded by a global ocean called
Panthalassa. The
CarboniferousCarboniferous rainforest collapse left behind vast
regions of desert within the continental interior.[6] Amniotes, who
could better cope with these drier conditions, rose to dominance in
place of their amphibian ancestors.
The
PermianPermian (along with the Paleozoic) ended with the
Permian–
TriassicTriassic extinction event, the largest mass extinction in
Earth's history, in which nearly 90% of marine species and 70% of
terrestrial species died out.[7] It would take well into the Triassic
for life to recover from this catastrophe.[8] Recovery from the
Permian–
TriassicTriassic extinction event was protracted; on land,
ecosystems took 30 million years to recover.[9]

Discovery[edit]
The term "Permian" was introduced into geology in 1841 by Sir R. I.
Murchison, president of the Geological Society of London, who
identified typical strata in extensive Russian explorations undertaken
with Édouard de Verneuil.[10][11] The region now lies in the Perm
Krai of Russia.
ICS Subdivisions[edit]
Official ICS 2017 subdivisions of the
PermianPermian System from most recent
to most ancient rock layers are:[12]

Oceans[edit]
Sea levels in the
PermianPermian remained generally low, and near-shore
environments were reduced as almost all major landmasses collected
into a single continent – Pangaea. This could have in part
caused the widespread extinctions of marine species at the end of the
period by severely reducing shallow coastal areas preferred by many
marine organisms.
Paleogeography[edit]

During the Permian, all the Earth's major landmasses were collected
into a single supercontinent known as Pangaea.
PangaeaPangaea straddled the
equator and extended toward the poles, with a corresponding effect on
ocean currents in the single great ocean ("Panthalassa", the
"universal sea"), and the Paleo-Tethys Ocean, a large ocean that was
between Asia and Gondwana. The Cimmeria continent rifted away from
GondwanaGondwana and drifted north to Laurasia, causing the Paleo-Tethys Ocean
to shrink. A new ocean was growing on its southern end, the Tethys
Ocean, an ocean that would dominate much of the
MesozoicMesozoic era. Large
continental landmass interiors experience climates with extreme
variations of heat and cold ("continental climate") and monsoon
conditions with highly seasonal rainfall patterns. Deserts seem to
have been widespread on Pangaea. Such dry conditions favored
gymnosperms, plants with seeds enclosed in a protective cover, over
plants such as ferns that disperse spores in a wetter environment. The
first modern trees (conifers, ginkgos and cycads) appeared in the
Permian.
Three general areas are especially noted for their extensive Permian
deposits – the
Ural MountainsUral Mountains (where
PermPerm itself is located),
China, and the southwest of North America, including the
TexasTexas red
beds. The
PermianPermian Basin in the U.S. states of
TexasTexas and
New MexicoNew Mexico is
so named because it has one of the thickest deposits of
PermianPermian rocks
in the world.
Climate[edit]

Selwyn Rock, South Australia, an exhumed glacial pavement of Permian
age

The climate in the
PermianPermian was quite varied. At the start of the
Permian, the
EarthEarth was still in an ice age, which began in the
Carboniferous. Glaciers receded around the mid-
PermianPermian period as the
climate gradually warmed, drying the continent's interiors.[14] In the
late
PermianPermian period, the drying continued although the temperature
cycled between warm and cool cycles.[14]
Life[edit]

Marine biota[edit]
PermianPermian marine deposits are rich in fossil mollusks, echinoderms, and
brachiopods.[15] Fossilized shells of two kinds of invertebrates are
widely used to identify
PermianPermian strata and correlate them between
sites: fusulinids, a kind of shelled amoeba-like protist that is one
of the foraminiferans, and ammonoids, shelled cephalopods that are
distant relatives of the modern nautilus. By the close of the Permian,
trilobites and a host of other marine groups became extinct.
Terrestrial biota[edit]
Terrestrial life in the
PermianPermian included diverse plants, fungi,
arthropods, and various types of tetrapods. The period saw a massive
desert covering the interior of Pangaea. The warm zone spread in the
northern hemisphere, where extensive dry desert appeared.[15] The
rocks formed at that time were stained red by iron oxides, the result
of intense heating by the sun of a surface devoid of vegetation cover.
A number of older types of plants and animals died out or became
marginal elements.
The
PermianPermian began with the
CarboniferousCarboniferous flora still flourishing.
About the middle of the
PermianPermian a major transition in vegetation
began. The swamp-loving lycopod trees of the Carboniferous, such as
LepidodendronLepidodendron and Sigillaria, were progressively replaced in the
continental interior by the more advanced seed ferns and early
conifers. At the close of the Permian, lycopod and equisete swamps
reminiscent of
CarboniferousCarboniferous flora survived only on a series of
equatorial islands in the
Paleo-Tethys OceanPaleo-Tethys Ocean that later would become
South China.[16]
The
PermianPermian saw the radiation of many important conifer groups,
including the ancestors of many present-day families. Rich forests
were present in many areas, with a diverse mix of plant groups. The
southern continent saw extensive seed fern forests of the Glossopteris
flora.
OxygenOxygen levels were probably high there. The ginkgos and cycads
also appeared during this period.
Insects[edit]
From the Pennsylvanian subperiod of the
CarboniferousCarboniferous period until
well into the Permian, the most successful insects were primitive
relatives of cockroaches. Six fast legs, four well-developed folding
wings, fairly good eyes, long, well-developed antennae (olfactory), an
omnivorous digestive system, a receptacle for storing sperm, a
chitin-based exoskeleton that could support and protect, as well as a
form of gizzard and efficient mouth parts, gave it formidable
advantages over other herbivorous animals. About 90% of insects at the
start of the
PermianPermian were cockroach-like insects
("Blattopterans").[17]
Primitive forms of dragonflies (Odonata) were the dominant aerial
predators and probably dominated terrestrial insect predation as well.
True
OdonataOdonata appeared in the Permian,[18][19] and all are effectively
semi-aquatic insects (aquatic immature stages, and terrestrial
adults), as are all modern odonates. Their prototypes are the oldest
winged fossils,[20] dating back to the Devonian, and are different in
several respects from the wings of other insects.[21]
FossilsFossils suggest
they may have possessed many modern attributes even by the late
Carboniferous, and it is possible that they captured small
vertebrates, for at least one species had a wing span of 71 cm
(28 in).[22] Several other insect groups appeared or flourished
during the Permian, including the
ColeopteraColeoptera (beetles) and Hemiptera
(true bugs).
SynapsidSynapsid and amphibian fauna[edit]
Early
PermianPermian terrestrial faunas were dominated by pelycosaurs,
diadectids and amphibians,[23][24] the middle
PermianPermian by primitive
therapsids such as the dinocephalia, and the late
PermianPermian by more
advanced therapsids such as gorgonopsians and dicynodonts. Towards the
very end of the
PermianPermian the first archosaurs appeared, a group that
would give rise to the crurotarsans and the dinosaurs in the following
period. Also appearing at the end of the
PermianPermian were the first
cynodonts, which would go on to evolve into mammals during the
Triassic. Another group of therapsids, the therocephalians (such as
Lycosuchus), arose in the Middle Permian.[25][26] There were no aerial
vertebrates (with the exception of gliding reptiles, the
avicephalans).
The
PermianPermian period saw the development of a fully terrestrial fauna
and the appearance of the first large herbivores and carnivores. It
was the high tide of the anapsids in the form of the massive
Pareiasaurs and host of smaller, generally lizard-like groups. A group
of small reptiles, the diapsids, started to abound. These were the
ancestors to most modern reptiles and the ruling dinosaurs as well as
pterosaurs and crocodiles.
The synapsid, early ancestors to mammals, also thrived at this time.
Synapsids included some large members such as Dimetrodon. The special
adaptations of reptiles enabled them to flourish in the drier climate
of the
PermianPermian and they grew to dominate the vertebrates.[23]
PermianPermian amphibians consisted of temnospondyli, lepospondyli and
batrachosaurs.

The Permian–
TriassicTriassic extinction event, labeled "End P" here, is the
most significant extinction event in this plot for marine genera which
produce large numbers of fossils.

Main article: Permian–
TriassicTriassic extinction event
The
PermianPermian ended with the most extensive extinction event recorded in
paleontology: the Permian–
TriassicTriassic extinction event. 90% to 95% of
marine species became extinct, as well as 70% of all land organisms.
It is also the only known mass extinction of insects.[8][27] Recovery
from the Permian-
TriassicTriassic extinction event was protracted; on land,
ecosystems took 30 million years to recover.[9] Trilobites, which had
thrived since
CambrianCambrian times, finally became extinct before the end of
the Permian. Nautiluses, a species of cephalopods, surprisingly
survived this occurrence.
There is evidence that magma, in the form of flood basalt, poured onto
the surface in what is now called the Siberian Traps, for thousands of
years, contributing to the environmental stress that led to mass
extinction. The reduced coastal habitat and highly increased aridity
probably also contributed. Based on the amount of lava estimated to
have been produced during this period, the worst-case scenario is the
release of enough carbon dioxide from the eruptions to raise world
temperatures five degrees Celsius.[14]
Another hypothesis involves ocean venting of hydrogen sulfide gas.
Portions of the deep ocean will periodically lose all of its dissolved
oxygen allowing bacteria that live without oxygen to flourish and
produce hydrogen sulfide gas. If enough hydrogen sulfide accumulates
in an anoxic zone, the gas can rise into the atmosphere. Oxidizing
gases in the atmosphere would destroy the toxic gas, but the hydrogen
sulfide would soon consume all of the atmospheric gas available.
Hydrogen sulfideHydrogen sulfide levels might have increased dramatically over a few
hundred years. Models of such an event indicate that the gas would
destroy ozone in the upper atmosphere allowing ultraviolet radiation
to kill off species that had survived the toxic gas.[28] There are
species that can metabolize hydrogen sulfide.
Another hypothesis builds on the flood basalt eruption theory. An
increase in temperature of five degrees Celsius would not be enough to
explain the death of 95% of life. But such warming could slowly raise
ocean temperatures until frozen methane reservoirs below the ocean
floor near coastlines melted, expelling enough methane (among the most
potent greenhouse gases) into the atmosphere to raise world
temperatures an additional five degrees Celsius. The frozen methane
hypothesis helps explain the increase in carbon-12 levels found midway
in the Permian–
TriassicTriassic boundary layer. It also helps explain why
the first phase of the layer's extinctions was land-based, the second
was marine-based (and starting right after the increase in C-12
levels), and the third land-based again.[29]
An even more speculative hypothesis is that intense radiation from a
nearby supernova was responsible for the extinctions.[30]
It has been hypothesised that huge meteorite impact crater (Wilkes
Land crater) with a diameter of around 500 kilometers in Antarctica
represents an impact event that may be related to the extinction.[31]
The crater is located at a depth of 1.6 kilometers beneath the ice of
Wilkes Land in eastern Antarctica. The scientists speculate that this
impact may have caused the Permian–
TriassicTriassic extinction event,
although its age is bracketed only between 100 million and 500 million
years ago. They also speculate that it may have contributed in some
way to the separation of Australia from the Antarctic landmass, which
were both part of a supercontinent called Gondwana. Levels of iridium
and quartz fracturing in the Permian-
TriassicTriassic layer do not approach
those of the Cretaceous–
Paleogene boundary layer. Given that a far
greater proportion of species and individual organisms became extinct
during the former, doubt is cast on the significance of a meteorite
impact in creating the latter. Further doubt has been cast on this
theory based on fossils in Greenland that show the extinction to have
been gradual, lasting about eighty thousand years, with three distinct
phases.[32]
Many scientists argue that the Permian–
TriassicTriassic extinction event was
caused by a combination of some or all of the hypotheses above and
other factors; the formation of
PangaeaPangaea decreased the number of
coastal habitats and may have contributed to the extinction of many
clades.[citation needed]
See also[edit]